(a) Technical Field
The present invention relates to an end-modified diene copolymer having excellent compatibility with reinforcing silica and a preparation method thereof. More particularly, the present invention relates to an end-modified diene copolymer prepared by preparing a living polymer of a conjugated diene monomer and/or a vinyl aromatic monomer, modifying the living polymer with a reactive organosiloxane compound, and then modifying the end of the living polymer, to which the organosiloxane compound has not been coupled, with an organosilane compound having various functional groups, and to a method for preparing the end-modified diene copolymer.
(b) Background Art
A diene polymer is commonly used as a raw material for rubber. A typical example of this diene polymer may be a butadiene polymer or a styrene-butadiene copolymer.
The diene polymer is generally prepared by a solution polymerization process in the presence of an organolithium catalyst. The solution polymerization process has an advantage in that molecular structures such as the vinyl structure of conjugated diene, the styrene block percentage, etc. can be easily controlled, unlike a conventional emulsion polymerization process. The diene polymer prepared by the solution polymerization process has significantly excellent rolling resistance and wet traction compared to a styrene-butadiene rubber (SBR) prepared by the emulsion polymerization process, and thus is suitable as a rubber material for manufacturing tires. In the solution polymerization process that is carried out in the presence of an organolithium catalyst, various functional groups can be easily introduced into the molecular end to control cold flow at room temperature and to improve processability and bonding strength when the polymer is compounded with an inorganic reinforcing material such as silica, thus improving the dispersibility of the reinforcing material. Additionally, various kinds of functional groups can be introduced into a polymer to increase compatibility with an inorganic reinforcing material for tires, thus improving wear resistance, reducing rolling resistance and increasing wet traction.
Conventional solution polymerization techniques for increasing compatibility with carbon black or silica as an inorganic reinforcing material will now be explained.
First, in an attempt to develop a method for increasing the compatibility of rubber with carbon black, U.S. Pat. No. 4,555,548 discloses a method for modifying the ends of the molecule with an amine compound such as amino benzophenone in order to obtain excellent dynamic properties and mechanical properties compared to those of conventional rubbers. However, the rubber prepared by this method, when compounded with an inorganic reinforcing material, has poor processability, and the cold flow of the rubber, which is an important factor for storage stability, is high, thus causing a problem associated with long-term storage. Particularly, if this rubber is used to manufacture a tire containing reinforcing silica (hereinafter, referred to as “silica tire”), the mechanical properties and dynamic properties (e.g., rolling resistance and wet traction) of the tire will be deteriorated due to the low compatibility of the rubber with silica. Thus, there is a limit in the use of the rubber for the manufacture of silica tires.
U.S. Pat. No. 6,329,467 describes a method of using a mixture of tin tetrachloride and silicon tetrachloride as a coupling agent to improve the processability and rolling resistance of a carbon black-containing composition. However, because the polymer prepared by this method has no functional group inducing compatibility with a reinforcing material, it has low compatibility with the reinforcing material in a silica-containing composition, indicating that it is difficult to prepare a rubber suitable for silica tires using the polymer. Particularly, when tin tetrachloride is used, there is a problem in that the properties of the silica-containing composition are deteriorated, because the bond between tin and the polymer is dissociated by stearic acid which is used as a vulcanization accelerator.
U.S. Pat. No. 6,133,388 discloses a technique of maximizing compatibility with a reinforcing material by modifying both ends of a molecule with functional groups. However, the compound thus prepared has increased viscosity in a solution, which makes it difficult to actually commercialize the compound.
In attempts to increase compatibility with silica that is an inorganic reinforcing material, Korean Patent Application Publication Nos. 94-019797 and 94-019795 disclose dispersing polydimethylsiloxane in a styrene-based resin composition to significantly improve the wear resistance and cold impact resistance of the composition. However, the polymer complex prepared by dispersing polydimethylsiloxane has no covalent bond between the polydimethylsiloxane and the organic polymer resin, and thus is likely to undergo phase separation. Also, because the polydimethylsiloxane has no polar group or hydrophilic group, the polymer complex has low compatibility with an inorganic reinforcing material.
In the development of organic/inorganic composite materials, the modification of organic polymers that are highly reactive has been performed to enhance the compatibility between the organic and inorganic materials, and many studies on techniques for modifying such inorganic polymers have been conducted. For example, Korean Patent Application Publication No. 95-704405 discloses a technique of polymerizing hexamethylcyclotrisiloxane at the end of a living polymer block. In addition, it was reported that, in order to enhance the miscibility between organic and inorganic composite materials, the end of a living polymer was modified with ethylene oxide (J. Polym. Sci., Part A: Polym. Chem., 26, 2031 (1988)), diphenylethylene (J. Polym. Sci., Part A: Polym. Chem., 30, 2349 (1992)), N-(benzylidene)-trimethylsilylamine (Makromol. Chem., 184, 1355 (1983)) or the like; however, there is a limit to obtain sufficient compatibility with inorganic fillers.
As described above, there is a demand for the development of a novel diene polymer which overcomes the shortcomings of conventional diene polymers and has excellent compatibility with inorganic fillers, and thus is suitable as a material for tires.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.